What is the need of using combination of resistance in electrical circuits? Define equivalent resistance.

Explanation

Combination of resistances is used in circuit so as to get the desired value of current in an electrical circuit.
i] Series combination
ii] Parallel combination
iii] Series-parallel combination.
Equivalent resistance:
If a single resistance can replace the combination of resistances in such a manner that the current in the circuit remains unchanged, then that single resistance is called the equivalent resistance.